添加和删除元素设置为HashMap中的值
所以我有一个看起来像这样的文件:添加和删除元素设置为HashMap中的值
1st 2nd nth
e1, v1, 1
e1, v3, 2
e1, v4, 4
e1, v5, 7
e2, v1, 1
., ., .
., ., .
., ., .
,我想的第一列是一个HashMap的关键(E1或e2或者e3),并且这个值是一个名为“Ratings”的ArrayList,我希望第二列在ArrayList的第n个索引内具有它的值(一个int)。
这里是我的代码在它的全部迄今:
import java.util.*;
import java.io.*;
public class Setup
{
public static void Setup(String[] args)
{
String user;
int value, location;
//Create a Hashmap that holds a string key and an ArrayList value
HashMap<String, ArrayList<Integer>> userRatings = new HashMap<String, ArrayList<Integer>>();
try
{
BufferedReader bufferReader = new BufferedReader(new FileReader("Student list.txt")); //read from file
String line, sentence; //declare two string variables
String[] sData; //declare a string array (store the contents here)
line = bufferReader.readLine(); //Read the line
while (line != null) //While there is a line, do this:
{
line = bufferReader.readLine();
sData = line.split(", "); //Into the string array, enter individual values in the line split by the ", " characters
int iData[] = new int[sData.length]; //Create an int array the size of the string array
user = sData[0];
for (int i = 0; i <sData.length; i++) //fill the int array with the int-version of the string array
{
iData[i] = Integer.parseInt(sData[i]); //pass the strings as integers into the integer array
}
value = iData[1];
location = iData[2];
if(!userRatings.containsKey(user)) //The user does not have ratings.
{
ArrayList<Integer> ratings = new ArrayList<Integer>();
// ratings = userRatings.get(user);
for (int j = 0; j < 50; j++)
{
ratings.add(j);
}
System.out.println(user + " " + userRatings.get(user));
}
else //The user has ratings
{
userRatings.get(user).add(location,value);
System.out.println(user + " " + userRatings.get(user));
}
}
bufferReader.close();
} catch (FileNotFoundException e)
{
System.out.println("File does not exist or could not be found.");
}
catch (IOException e)
{
System.out.println("Can't read from file");
}
catch (NullPointerException e)
{
}
}
}
我有修改的ArrayList内容的问题。
综上所述: 在文件的第1列的每个字符串必须是在HashMap中(用户列表) 程序会检查是否有钥匙,如果没有键存在,它会创建一个新的自己的钥匙arraylist作为密钥的值。 arrayList将填充50个索引,其中将包含“0”。 之后,ArrayList将从文件中添加新值,其中第二列中的整数将被添加到第n列的对应值。
我该如何填充arraylist,以及如何编辑它,以便如果我想在用户e6的第n个索引处添加新的整数,我可以?
当给定的键不存在在你的地图,你必须添加一个新的键值对
if(!userRatings.containsKey(user)) //The user does not have ratings.
{
ArrayList<Integer> ratings = new ArrayList<Integer>();
for (int j = 0; j < 50; j++) {
ratings.add(j);
}
userRatings.put(user, ratings); // place new mapping
System.out.println(user + " " + userRatings.get(user));
} else //The user has ratings
{
ArrayList<Integer> ratings = userRatings.get(user);
ratings.add(location,value); // Update your list with location and value
System.out.println(user + " " + userRatings.get(user));
}
iData[i] = Integer.parseInt(sData[i]);
这是不行的给你的文件的内容会抛出NumberFormatException
为V1不能被解析为int。
相反,你可以做这样的事情:
value = Integer.parseInt(sData[1].trim().substring(1));
location = Integer.parseInt(sData[2].trim());
比较两个键的值:
方法1
ArrayList<Integer> first = userRatings.get(e1);
ArrayList<Integer> second = userRatings.get(e2);
//Taking the smallest size will ensure that we don't get IndexOutOfBoundsException.
int length = first.size() < second.size() ? first.size() : second.size();
for(int iDx = 0; iDx < legth; iDx++){
//compare content
}
方法2
ArrayList<Integer> first = userRatings.get(e1);
ArrayList<Integer> second = userRatings.get(e2);
Arrays.equals(first.toArray(), second.toArray());
我想你可以阅读第n个值并使用它将值插入列表中。
例如
List<Integer> list = new ArrayList<Integer>();
//values values (0) will be inserted into the list
//after that for each value in the nth you do something as follows
//i is the value in the nth column, if the least value for i is 1 otherwise just use i
list.add(i-1, value);
也为参考使用界面,而不是实施类如下 -
Map<String, List<Integer>> userRatings = new HashMap<String, List<Integer>>();
List<Integer> ratings = new ArrayList<Integer>();
要插入值到第n个指标为用户E6:
List<Integer> ratings = userRatings.get(user);
if(ratings == null) {
ratings = new ArrayList<Integer>(); //it's not in the map yet
//insert 50 0s here
userRatings.put(user, ratings);
}
ratings.add(i, value); //i is the nth index and value is the rating
然而,这太好了,做了什么mprabhat建议很简单,我尝试了它,并让它按我的想象工作!谢谢你的回答!你帮助我更好地理解了这个概念,并为以后的不同方法提供了想法。 –
谢谢@mprabhat!这很棒!很简单,我没有这样想过,但这很有道理!拿出来,编辑它,然后放回去。 如果我要比较两个不同的键的值,我将如何处理? 即我想比较e1的阵列列表和e2的阵列列表。 –
如果你想比较两个ArrayList,那么你将不得不循环检查并逐一比较内容。 – mprabhat
另一种方法是将两个ArrayList转换为Array,然后调用[Arrays.equals](http://docs.oracle.com/javase/6/docs/api/java/util/Arrays.html) – mprabhat